Cunninghamia : A Journal of Plant Ecology for Eastern Australia, Volume 6, Issue 1 (1999)
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An exhaustive review of available information revealed 1522 native vascular plant taxa with confirmed records in the Eden region. A further 136 taxa potentially occur in the region, but these remain to be confirmed. Families represented by large numbers of taxa in the indigenous flora include the Fabaceae, Poaceae, Asteraceae, Myrtaceae and Orchidaceae. Species frequencies were highly skewed with 74% of the flora represented in less than 1% of survey samples and only three taxa represented in more than 40% of samples. A large number of records (350 taxa) were evaluated and refuted, emphasizing the importance of critical validation when compiling biological inventory data from multiple sources. Errors are most likely to arise from nomenclatural synonymy and other duplications, misidentifications and erroneous locality information.
The confirmed vascular flora of the Eden region is relatively species-rich compared with other regions in tropical, temperate and semi-arid Australia, although these regions are less well-known botanically. However, the proportion of endemism (1%) is comparatively low, with 18 taxa unique to the region and a further 14 taxa with distributions extending just beyond the region. The Eden region includes 32 taxa listed as endangered or vulnerable in Australia and a further six taxa listed as endangered in New South Wales but not throughout Australia. Thirty-eight taxa were listed as rare in Australia and a further 39 were considered to be uncommon throughout their distribution. Four hundred and sixty-six taxa were considered to be uncommon within the Eden region. Two hundred and seventy-six taxa reached their distributional limits in the Eden region, about three quarters of these reaching their southern limits. Fifty taxa were represented in the region by disjunct populations.
Introduced taxa accounted for approximately 20% of the total regional vascular flora, although this proportion is likely to underestimate the introduced flora given the limitations of available data. The introduced flora is dominated by Poaceae, Asteraceae, Fabaceae and Caryophyllaceae. Very few introduced taxa were widespread in native vegetation. The most common introduced taxa were herbs with long-distance propagule dispersal mechanisms.
Terrestrial, freshwater and estuarine native vegetation of the Eden region was classified into 79 floristic assemblages and mapped at 1:100,000 scale. Assemblages were derived from multivariate analysis of 1604 quantitative vegetation samples. Mapping was carried out using a hybrid decision tree-expert system approach based on quantitative relationships between floristic assemblages and spatial variables (land cover pattern, substrate, climatic variables and terrain variables) and qualitative expert knowledge derived from field experience. The use of vegetation environment relationships and sampling of remnants allowed prediction of vegetation patterns prior to European clearing. The map was validated using three procedures: qualitative checking by experts; reliability mapping using sampling intensity; and accuracy quantification using independent sample data. The map units were described using comprehensive profiles of diagnostic species, structural features, habitat characteristics and sample distributions.
The 79 floristic assemblages include rainforests, mesic eucalypt forests, dry grassy eucalypt forests of the coastal rain shadow valleys, hinterland and tableland, dry shrubby eucalypt forests, grasslands, heathlands, scrubs and wetlands. Variation in climate and geological substrate influence vegetation patterns at regional scales, while variation in topography, local soil moisture and nutrient status and disturbance regimes influence vegetation patterns at local scales. Sixty-eight per cent of the region retained a cover of native vegetation in 1994. Processes threatening various portions of the remainder include further habitat loss from clearing, high-frequency disturbances and certain other disturbance regimes, overgrazing, habitat degradation due to nutrification, dumping and vandalism, and feral animal activity. Past depletion of habitat has been highly biased. Some grassy assemblages on fertile flat terrain are depleted by more than 90%, while some forests with shrubby understories in steep infertile terrain retain close to their original extent. The former assemblages are distributed principally as remnants on privately owned land, while the latter occur in remote areas of public land. Representation in conservation reserves is also biased against grassy assemblages in fertile flat terrain, as well as some other assemblages with restricted distributions. Opportunities for conservation of these assemblages are now very limited and rely on integrated planning, reservation and cooperative management with emphasis on private land.